Recent literature has indicated an increasing incidence of right heart failure in patients dying following cardiovascular surgery in which left ventricular assist devices have been employed to support their failing left ventricle. Those patients whose right hearts were also supported with an assist device exhibited improved cardiac output and several patients have recovered after several days of biventricular assist. The research described in this application is intended to investigate the cause of unilateral right heart failure. We propose to test the following hypothesis: "Unilateral right ventricular failure following cardiopulmonary bypass will result if right ventricular temperature increases excessively during the elective ischemia of heart surgery while left ventricular temperature is maintained at a level sufficiently low to insure preservation of left ventricular function." Twenty-five experiments on dogs (5 groups of 5 experiments each) are proposed to test this hypothesis. Right ventricular temperature will be preferentially increased to values higher than the left ventricular temperature during 90 minutes of myocardial ischemia, and pre- and post-ischemic right and left ventricular function will be compared. (Tleft ventricle = 15 C in all experiments). The investigation is also designed to establish the maximum right ventricular-left ventricular temperature difference which may be tolerated during the elective ischemia of heart surgery without danger of unilateral right ventricular failure.